This invention relates to a novel fixture for holding a faceplate and a funnel of a CRT (cathode-ray tube) during the time that they are being sealed together, and particularly to such a fixture which has improved structures for aligning the faceplate and funnel with respect to each other.
One type of CRT comprises a glass envelope that is fabricated by sealing the faceplate to the funnel after the viewing screen and other internal structures have been assembled to these parts. In one common practice, a bead of frit material, which is typically a devitrifying glass, is applied to the sealing land of one of the faceplate and the funnel. The sealing land of the other part is then placed in contact with the bead, thereby abutting the sealing land of the one part. The abutting faceplate and funnel which can be in either the faceplate-up or faceplate-down position, are then heated and cooled to cause the frit to hermetically seal the panel and funnel together.
Various fixtures have been described for holding and supporting the faceplate and funnel in aligned abutting relationship during sealing; that is, while they are being heated and cooled. Generally, the fixture comprises a base, a means on the base for supporting a faceplate and a funnel in abutting relationship, and a plurality of alignment structures so attached to and positioned on the supporting means that the faceplate and funnel are in alignment when they bear against prescribed surfaces of the alignment structures.
In prior fixtures, each alignment structure comprises a pair of alignment fingers or pins mounted on a support and extending radially inwardly. The inward surfaces of the fingers are the prescribed surfaces that the faceplate and funnel bear against when they are in alignment. The use of fingers or pins for alignment has several disadvantages. One disadvantage is that they wear rapidly because of the small surface areas that are involved and because of the heating and cooling that they are exposed to. This requires constant checking and readjustment in order to assure the proper faceplate and funnel alignment. In those fixtures in which screws are used to adjust the positions of the fingers, the screws may rotate out of adjustment due to vibration of the fixture during sealing.